This invention relates to fans which are used to move air through a heat exchanger.
Such fans customarily have a hub which is rotated about its axis, for example by an electric motor or by an engine, and a plurality of blades extending radially from the hub. The blades are pitched at an angle to pump air when rotated, and that air is either blown through a heat exchanger, if the heat exchanger is on the high-pressure (downstream) side of the fan, or drawn through the heat exchanger, if the exchanger is on the low-pressure (upstream) side of the fan.
The air flow generated by the fan is relatively complex. As the blades rotate, air is driven in a direction oblique to the axis (i.e., at an angle between the radial plane of the fan and the fan axis). Thus, the fan exhaust has both an axial component and a rotational component imposed by the blades. Struts which support the motor also deflect the airflow. Finally, vortices which form at the fan blade tips further complicate the air flow.
In many applications, one or more of these efficiency-reducing factors results in relatively higher design costs because of the need for greater fan-rotating power and/or additional design and manufacturing features.
McMahan U.S. Pat. No. 2,154,313 discloses a fan for blowing air through a heat exchanger. A set of vanes is positioned on the downstream side of the fan blades to correct the variation in velocity at different radial positions by radially deflecting the airflow exiting the fan blades. The resulting more radially uniform air flow velocity is intended to improve efficiency of the heat exchanger.
Koch U.S. Pat. No. 2,628,019 discloses a free-standing fan having vanes to concentrate the air flow to maintain velocity and reduce diffusion.
Gray U.S. Pat. No. 4,358,245 discloses a fan for drawing air through a radiator; the fan includes a circumferential band around the blade tips, and a shroud which reduces recirculation of air around the outer edge of the fan.